This invention relates to improvements in lubricated compressor cylinders of the reciprocating plunger type. More particularly, it is directed to an improved lubrication system for such compressor cylinders involving modified packing cup elements especially adapted for use in the annular seal assemblies thereof.
Reciprocating compressors have been developed extensively in order to provide various commercial operations, e.g. polyethylene manufacturing, with feed streams at the elevated pressures required, e.g. around 1000 atmospheres and above. In order to achieve commercially practical performance, much effort has been applied towards minimizing two basic engineering problems which are virtually inherent in reciprocal hyper-compression, namely (1) fatigue failures in components subject to cyclic pressure fluctuations and (2) maintenance difficulties with high pressure seals, particularly around the periphery of the reciprocating plunger rod.
In order to provide adequate and serviceable sealing around the periphery of the plunger, it has been common practice to employ an axial series of close-fitting annular packing cups with inner peripheral recesses therein in which are carried specially shaped and fitted seal rings. The assembled series of packing cups is rigidly mounted to provide a cylindrical bore surrounding the plunger rod with the seal rings bearing against the periphery thereof. In order to reduce frictional effects and wear, a lubricating liquid is normally fed to the periphery of said plunger at one or more locations, e.g. as shown in U.S. Pat. No. 3,490,774 to Henry et al.
Many different approaches have been applied in dealing with the aforementioned fatigue problems, including the use of autofrettage treatments, shrink fit constructions and similar methods of insuring that critical parts are maintained in compression throughout the working cycle. For example, FIG. 1 of the above mentioned U.S. Pat. No. 3,490,774 depicts a seal assembly in which most of the packing cups (i.e. 40-46) are of the familiar compound construction comprising an inner (a) ring onto which an outer (b) ring is shrink-fitted.
An alternative approach which has found commercial utility in this field is to subject the outer periphery of the seal assembly to the actual working fluid of the compressor at substantially full discharge pressure as disclosed in U.S. Pat. No. 3,128,941 to Waibel. As depicted in FIG. 4 of said patent, this so-called "pressure-wrapped" seal assembly design permits the use of simpler, unitary packing cups which are automatically maintained largely under compressive stress by the working fluid during the actual operation of the compressor.
Through the adoption of such special measures, the susceptibility of the packing cups in reciprocating compressors to suffer fatigue failures has been greatly alleviated in recent years. However, difficulty is still being experienced in translating these gains in packing cup fatigue resistance into extended on-line uninterrupted compressor service because of fatigue failures occuring in certain associated components of the compressor which necessitate shut downs for repairs. Notable among the auxiliary components showing greatest vulnerability in this respect are the bottom end spacer at the crank end of the compressor cylinder and the lubricant feed quills, check valves and other elements of the lubricating system.
The primary object of the present invention is to improve the reliability and service life of the lubrication system for a reciprocating compressor. A closely allied object is to integrate the lubricating system into the annular seal assembly of a reciprocating plunger compressor to form a more durable and efficient overall machine, thus providing extended on-line service life for the entire compressor.
Still other objects and related advantages of the present invention will become apparent from the following detailed description thereof.